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1.
PLoS One ; 19(4): e0299688, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38635645

RESUMO

With the world population growth, energy consumption and the rapid development of industrial economy, a large amount of carbon emissions has brought destruction and threats to the earth's environment on which human beings depend. The development of low-carbon economy has become the consensus of governments all over the world and has been vigorously advocated & promoted. This paper focuses on the top five global GDP nations in 2022: The United States, China, Japan, Germany, and Britain. A comprehensive evaluation index system of urban low-carbon economic development level is constructed from four dimensions: economic development level, environmental quality, energy consumption emission intensity and social development speed by using literature review and field interview. The evaluation measures are determined using the TOPSIS evaluation method with entropy weight and the grey relational model, providing a comprehensive assessment of the low-carbon economy's development level in these five countries." Judging from the comprehensive evaluation score, the overall development of low-carbon economy in American cities is in good condition and has reached the development standard of low-carbon economy; Germany and Japan rank second and third, and they are low-carbon economies. Britain ranks fourth in comprehensive evaluation, although it belongs to a low-carbon economy country, but there is still a certain gap with Germany and Japan; There is still a big gap between China and the other four countries. Based on the measurement and evaluation outcomes, it presents recommendations and strategies to foster the growth of low-carbon economies, offering valuable insights for the advancement of such economies across different nations. The research results guide countries all over the world to reduce carbon emissions in the process of economic development, protect the earth environment on which human beings depend, and make a better tomorrow for sustainable development.


Assuntos
Carbono , Desenvolvimento Econômico , Humanos , China , Cidades , Consenso , Dióxido de Carbono
2.
Behav Res Methods ; 2024 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-38528247

RESUMO

Questionnaires are ever present in survey research. In this study, we examined whether an indirect indicator of general cognitive ability could be developed based on response patterns in questionnaires. We drew on two established phenomena characterizing connections between cognitive ability and people's performance on basic cognitive tasks, and examined whether they apply to questionnaires responses. (1) The worst performance rule (WPR) states that people's worst performance on multiple sequential tasks is more indicative of their cognitive ability than their average or best performance. (2) The task complexity hypothesis (TCH) suggests that relationships between cognitive ability and performance increase with task complexity. We conceptualized items of a questionnaire as a series of cognitively demanding tasks. A graded response model was used to estimate respondents' performance for each item based on the difference between the observed and model-predicted response ("response error" scores). Analyzing data from 102 items (21 questionnaires) collected from a large-scale nationally representative sample of people aged 50+ years, we found robust associations of cognitive ability with a person's largest but not with their smallest response error scores (supporting the WPR), and stronger associations of cognitive ability with response errors for more complex than for less complex questions (supporting the TCH). Results replicated across two independent samples and six assessment waves. A latent variable of response errors estimated for the most complex items correlated .50 with a latent cognitive ability factor, suggesting that response patterns can be utilized to extract a rough indicator of general cognitive ability in survey research.

3.
BMJ Open ; 14(3): e079241, 2024 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-38453191

RESUMO

OBJECTIVES: This paper examined the magnitude of differences in performance across domains of cognitive functioning between participants who attrited from studies and those who did not, using data from longitudinal ageing studies where multiple cognitive tests were administered. DESIGN: Individual participant data meta-analysis. PARTICIPANTS: Data are from 10 epidemiological longitudinal studies on ageing (total n=209 518) from several Western countries (UK, USA, Mexico, etc). Each study had multiple waves of data (range of 2-17 waves), with multiple cognitive tests administered at each wave (range of 4-17 tests). Only waves with cognitive tests and information on participant dropout at the immediate next wave for adults aged 50 years or older were used in the meta-analysis. MEASURES: For each pair of consecutive study waves, we compared the difference in cognitive scores (Cohen's d) between participants who dropped out at the next study wave and those who remained. Note that our operationalisation of dropout was inclusive of all causes (eg, mortality). The proportion of participant dropout at each wave was also computed. RESULTS: The average proportion of dropouts between consecutive study waves was 0.26 (0.18 to 0.34). People who attrited were found to have significantly lower levels of cognitive functioning in all domains (at the wave 2-3 years before attrition) compared with those who did not attrit, with small-to-medium effect sizes (overall d=0.37 (0.30 to 0.43)). CONCLUSIONS: Older adults who attrited from longitudinal ageing studies had lower cognitive functioning (assessed at the timepoint before attrition) across all domains as compared with individuals who remained. Cognitive functioning differences may contribute to selection bias in longitudinal ageing studies, impeding accurate conclusions in developmental research. In addition, examining the functional capabilities of attriters may be valuable for determining whether attriters experience functional limitations requiring healthcare attention.


Assuntos
Envelhecimento , Cognição , Idoso , Humanos , Atenção , Estudos Longitudinais , Projetos de Pesquisa , Pessoa de Meia-Idade
4.
Autophagy ; : 1-20, 2023 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-38037248

RESUMO

Renal fibrosis is a typical pathological change in chronic kidney disease (CKD). Epithelial-mesenchymal transition (EMT) is the predominant stage. Activation of macroautophagy/autophagy plays a crucial role in the process of EMT. Lycopene (LYC) is a highly antioxidant carotenoid with pharmacological effects such as anti-inflammation, anti-apoptosis and mediation of autophagy. In this study, we demonstrated the specific mechanism of LYC in activating mitophagy and improving renal fibrosis. The enrichment analysis results of GO and KEGG showed that LYC had high enrichment values with autophagy. In this study, we showed that LYC alleviated aristolochic acid I (AAI)-induced intracellular expression of PINK1, TGFB/TGF-ß, p-SMAD2, p-SMAD3, and PRKN/Parkin, recruited expression of MAP1LC3/LC3-II and SQSTM1/p62, decreased mitochondrial membrane potential (MMP), and ameliorated renal fibrosis in mice. When we simultaneously intervened NRK52E cells using bafilomycin A1 (Baf-A1), AAI, and LYC, intracellular MAP1LC3-II and SQSTM1 expression was significantly increased. A similar result was seen in renal tissue and cells when treated in vitro and in vivo with CQ, AAI, and LYC, and the inhibitory effect of LYC on the AAI-activated SMAD2-SMAD3 signaling pathway was attenuated. Molecular docking simulation experiments showed that LYC stably bound to the AKT active site. After intervention of cells with AAI and GSK-690693, the expression of PINK1, PRKN, MAP1LC3-II, BECN1, p-SMAD2 and p-SMAD3 was increased, and the expression of SQSTM1 was decreased. However, SC79 inhibited autophagy and reversed the inhibitory effect of LYC on EMT. The results showed that LYC could inhibit the AKT signaling pathway to activate mitophagy and reduce renal fibrosis.Abbreviation: AA: aristolochic acid; ACTA2/α-SMA: actin alpha 2, smooth muscle, aorta; ACTB: actin beta; AKT/protein kinase B: thymoma viral proto-oncogene; BAF-A1: bafilomycin A1; BECN1: beclin 1, autophagy related; CCN2/CTGF: cellular communication network factor 2; CDH1/E-Cadherin: cadherin 1; CKD: chronic kidney disease; COL1: collagen, type I; COL3: collagen, type III; CQ: chloroquine; ECM: extracellular matrix; EMT: epithelial-mesenchymal transition; FN1: fibronectin 1; LYC: lycopene; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MMP: mitochondrial membrane potential; MTOR: mechanistic target of rapamycin kinase ; PI3K: phosphoinositide 3-kinase; PINK1: PTEN induced putative kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; PPI: protein-protein interaction; SMAD2: SMAD family member 2; SMAD3: SMAD family member 3; SQSTM1/p62: sequestosome 1; TGFB/TGFß: transforming growth factor, beta; VIM: vimentin.

5.
J Enzyme Inhib Med Chem ; 38(1): 2281893, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-37965884

RESUMO

In this study, a series of potential ligands for the treatment of AD were synthesised and characterised as novel harmine derivatives modified at position 9 with benzyl piperazinyl. In vitro studies revealed that the majority of the derivatives exhibited moderate to potent inhibition against hAChE and Aß1 - 42 aggregation. Notably, compounds 13 and 17d displayed potent drug - likeness and ADMET properties, demonstrating remarkable inhibitory activities towards AChE (IC50 = 58.76 nM and 89.38 nM, respectively) as well as Aß aggregation (IC50 = 9.31 µM and 13.82 µM, respectively). More importantly, compounds 13 and 17d showed exceptional neuroprotective effects against Aß1 - 42-induced SH - SY5Y damage, while maintaining low toxicity in SH - SY5Y cells. Further exploration of the mechanism through kinetic studies and molecular modelling confirmed that compound 13 could interact with both the CAS and the PAS of AChE. These findings suggested that harmine derivatives hold great potential as dual - targeted candidates for treating AD.


Assuntos
Doença de Alzheimer , Fármacos Neuroprotetores , Humanos , Doença de Alzheimer/tratamento farmacológico , Peptídeos beta-Amiloides , Acetilcolinesterase/metabolismo , Harmina/farmacologia , Harmina/uso terapêutico , Inibidores da Colinesterase/farmacologia , Cinética , Desenho de Fármacos , Relação Estrutura-Atividade , Fármacos Neuroprotetores/farmacologia
6.
Opt Express ; 31(2): 1049-1066, 2023 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-36785148

RESUMO

Microelectromechanical system (MEMS) mirror based laser beam scanning (LBS) projectors for fringe projection profilometry (FPP) are becoming increasingly popular attributing to their small size and low cost. However, the initial phase of the scanning MEMS mirror employed in an LBS projector may vary over time, resulting in unstable and distorted fringe patterns. The distorted fringe patterns will largely decrease the accuracy of the three-dimensional (3D) topographic reconstruction. In this paper, an efficient phase delay calibration method based on a unique fringe projection sequence and a corresponding image processing algorithm is proposed. The proposed method can compensate the phase uncertainty and variation with no need to add any extra components. One LBS projector has been constructed using a uniaxial electrostatic MEMS mirror that has a mirror size of 2.5 mm × 2.5 mm and a scanning field of view of 60 ∘ at its resonance of 1523 Hz. 3D reconstruction experiments are conducted to study how the 3D reconstruction results are affected by the phase delay. The standard deviation of a sphere reconstruction is improved from 2.05 mm to 0.20 mm after the positive phase delay deviation of 5 µs is compensated using this new calibration method.

7.
Redox Biol ; 57: 102494, 2022 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-36198206

RESUMO

Lycopene (LYC) is a carotenoid, has antioxidant properties. This study investigated whether lycopene attenuates aristolochic acids (AAs) -induced chronic kidney disease. In this experiment, lycopene was used to intervene C57BL/6 mice with renal injury induced by aristolochic acid exposure. The histomorphological changes and serological parameters of the kidney were measured in order to assess the alleviating effect of lycopene on renal injury in aristolochic acid nephropathy. In vitro and in vivo experiments were carried out to verify the main mechanism of action and drug targets of lycopene in improving aristolochic acid nephropathy (AAN) and by various experimental methods such as ELISA, immunohistochemistry, immunofluorescence, Western-blot and qRT-PCR. The results showed that oxidative stress injury was induced in the kidney of mice after AAI exposure, resulting in inflammatory response and tubular epithelial cell apoptosis. The results showed that the Nrf2/HO-1 antioxidant signaling pathway was inhibited after AAI exposure. AAI induces oxidative stress injury in the kidney, which ultimately leads to inflammation and tubular epithelial cell apoptosis. After LYC intervened in the body, it activated Nrf2 nuclear translocation and its downstream HO-1 and NQO1 antioxidant signaling pathways. LYC inhibited ROS production by renal tubular epithelial cells, and alleviated mitochondrial damage. LYC further modulated the TNF-α/NF-κB signaling cascade, thereby reduced the accumulation of inflammatory factors in the renal interstitium. Moreover, LYC was able to up-regulate the expression of Bcl-2, down-regulate Bax expression and inhibit the activation of cleaved forms of Caspase-9 and Caspase-3, which finally attenuated the apoptosis of the mitochondrial pathway induced by AAI exposure. It was concluded that lycopene was able to activate the Nrf2 antioxidant signaling pathway to maintain the homeostasis of renal oxidative stress and ultimately attenuated renal inflammatory response and apoptosis. These results suggested that lycopene can be used as a drug to relieve AAN.

8.
Toxicology ; 479: 153297, 2022 09.
Artigo em Inglês | MEDLINE | ID: mdl-36037877

RESUMO

Aristolochic acid I (AA-I), presenting in a variety of natural medicinal plants, which could cause tubular epithelial cell injury. Curcumin (CUR), a polyphenolic substance isolated from turmeric, is a natural antioxidant. The aim of this experiment was to investigate whether CUR attenuated AA-I-induced renal injury in rats through the SIRT1/Nrf2/HO-1 signaling pathway. SD rats were treated with AA-I (10 mg/kg) or/and CUR (200 mg/kg) for 28 days to assess the protective effect of CUR on AA-I-induced renal injury in vivo. NRK-52E cells were treated with AA-I (40 µ M) or/and CUR (20 µ M) for 24 h in vitro. The intervention pathway of CUR against oxidative stress injury induced by AA-I was assessed by observing pathological changes, oxidative stress status, apoptosis and the expression of SIRT1/Nrf2/HO-1 signaling pathway-related factors. The results showed that AA-I exposure increased the contents of BUN, Cr, KIM-1, NGAL, ALT and AST in serum. It increased the content of MDA, decreased the activities of SOD, GST, GSH and the content of ATP in renal tissue. Pathological changes such as inflammatory cell infiltration and mitochondrial injury occurred in renal tissue. AA-I exposure resulted in a substantial rise in the levels of BAX, Ccaspase-9, Cleaved Caspase-9, Caspase-3, Cleaved Caspase-3 and a significant decrease in mRNA and protein expression levels of Bcl-2, SIRT1, Nrf2, NQO1, HO-1 and Keap1. However, these changes were reversed by CUR intervention. In summary, AA-I exposure caused mitochondrial dysfunction and triggered apoptosis through the oxidative stress pathway. However, CUR could reduce AA-I-induced renal injury by activating the SIRT1/Nrf2/HO-1 signaling pathway.


Assuntos
Curcumina , Nefropatias , Fator 2 Relacionado a NF-E2 , Trifosfato de Adenosina/metabolismo , Animais , Antioxidantes/farmacologia , Apoptose , Ácidos Aristolóquicos/toxicidade , Caspase 3/metabolismo , Caspase 9/metabolismo , Curcumina/farmacologia , Proteína 1 Associada a ECH Semelhante a Kelch/metabolismo , Nefropatias/induzido quimicamente , Nefropatias/tratamento farmacológico , Lipocalina-2 , Fator 2 Relacionado a NF-E2/metabolismo , Estresse Oxidativo , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-Dawley , Transdução de Sinais , Sirtuína 1/metabolismo , Superóxido Dismutase/metabolismo , Proteína X Associada a bcl-2/metabolismo
9.
ACS Omega ; 6(13): 9129-9140, 2021 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-33842782

RESUMO

In this study, using molybdenum sulfide (MoS2) as laser-sensitive particles and poly(propylene) (PP) as the matrix resin, laser-markable PP/MoS2 composite materials with different MoS2 contents ranging from 0.005 to 0.2% were prepared by melt-blending. A comprehensive analysis of the laser marking performance of PP/MoS2 composites was carried out by controlling the content of laser additives, laser current intensity, and the scanning speed of laser marking. The color difference test shows that the best laser marking performance of the composite can be obtained at the MoS2 content of 0.02 wt %. The surface morphology of the PP/MoS2 composite material was observed after laser marking using a metallographic microscope, an optical microscope, and a scanning electron microscope (SEM). During the laser marking process, the laser energy was absorbed and converted into heat energy to cause high-temperature melting, pyrolysis, and carbonization of PP on the surface of the PP/MoS2 composite material. The black marking from carbonized materials was formed in contrast to the white matrix. Using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and Raman spectroscopy, the composite materials before and after laser marking were tested and characterized. The PP/MoS2 composite material was pyrolyzed to form amorphous carbonized materials. The effect of the laser-sensitive MoS2 additive on the mechanical properties of composite materials was investigated. The results show that the PP/MoS2 composite has the best laser marking property when the MoS2 loading content is 0.02 wt %, the laser marking current intensity is 11 A, and the laser marking speed is 800 mm/s, leading to a clear and high-contrast marking pattern.

10.
ACS Omega ; 6(8): 5764-5774, 2021 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-33681615

RESUMO

This study aimed to reveal the interaction between self-assembled multilayers and dye molecules in the environment, which is closely related to the multilayers' stable performance and service life. In this work, the pH-responsive poly (N-isopropylacrylamide-co-2-(dimethylamino) ethyl methacrylate) microgels were prepared by free-radical copolymerization and self-assembled with sodium alginate (SA) into multilayers by the layer-by-layer deposition method. Quartz crystal microbalance (QCM) and atomic force microscopy (AFM) results confirmed the construction of multilayers and the absorbed mass, resulting in a decrease in the frequency shift of the QCM sensor and the deposition of microgel particles on its surface. The interaction between the self-assembled SA/microgel multilayers and anionic dyes in the aqueous solution was further investigated by QCM, and it was found that the electrostatic attraction between dyes and microgels deposited on the QCM sensor surface was much larger than that of the microgels with SA in multilayers, leading to the release of the microgels from the self-assembled structure and a mass loss ratio of 27.6%. AFM observation of the multilayer morphology exposed to dyes showed that 29% of the microgels was peeled off, and the corresponding microgel imprints were generated on the surface. In contrast, the shape and size of the remaining self-assembled microgel particles did not change.

11.
ACS Omega ; 5(30): 19247-19254, 2020 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-32775928

RESUMO

In this work, poly(ethylene terephthalate) (PET) chain-extending products with different molecular weights were prepared by reactive extrusion using isocyanate trimer (C-HK) as the trifunctional chain extender. The effect of the chain extender C-HK on the intrinsic viscosity, melt flow property, crystallization behavior, crystallization morphology, and mechanical property of PET was investigated. The results showed that when the content of the chain extender was increased from 0.6 to 1.4 wt%, the viscosity average molecular weight of PET was effectively increased from 2.36 × 104 to 5.46 × 104 g·mol-1. After the chain extending, the crystallinity and the time of semicrystallization of PET were significantly decreased. After the isothermal crystallization at 220 °C for 5 min, the spherulites formed by pure PET became larger. With the increase in molecular weight of PET after chain extension, its spherulite size was significantly decreased without changing the crystalline structure. The chain-extended PET also exhibited more excellent bending-resistant and impact-resistant properties. While the tensile strength of PET after chain extension was slightly decreased, the bending strength was increased by a maximum value of 56.8%, and the impact strength was increased by a maximum value of five times.

12.
ACS Omega ; 5(30): 19255-19267, 2020 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-32775929

RESUMO

In this study, organically modified montmorillonite (OMMT) was prepared by modifying MMT with a cationic surfactant cetyltrimethylammonium bromide (CTAB). The obtained OMMT of different loading contents (1, 2, 4, 6, and 8 wt %) was melt-blended with poly(acrylonitrile-co-butadiene-co-styrene) (ABS) to prepare a series of ABS/OMMT composites, which were laser marked using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser beam of 1064 nm under different laser current processes. X-ray diffraction (XRD), color difference spectrometer, optical microscope, water contact angle tests, scanning electron microscope (SEM), and Raman spectroscopy were carried out to characterize the morphology, structure, and properties of the laser-patterned ABS composites. The effects of the addition of OMMT and the laser marking process on the mechanical properties of ABS/OMMT composites were investigated through mechanical property tests. The results show that the obtained ABS/OMMT composites have enhanced laser marking performance, compared to the ABS. When the OMMT content is 2 wt % and the laser current intensity is 9 A, the marking on ABS composites has the highest contrast (ΔE = 36.38) and sharpness, and the quick response (QR) code fabricated can be scanned and identified with a mobile app. SEM and water contact angle tests showed that the holes, narrow cracks, and irregular protrusion are formed on the composite surface after laser marking, resulting in a more hydrophobic surface and an increased water contact angle. Raman spectroscopy and XRD indicate that OMMT can absorb the near-infrared laser energy, undergo photo thermal conversion, and cause the pyrolysis and carbonization of ABS to form black marking, and the crystal structure itself does not change significantly. When the 2 wt % of OMMT is loaded, the tensile strength, elongation at break, and impact strength of ABS/OMMT are increased by 15, 20, and 14%, respectively, compared to ABS. Compared with the unmarked ABS/OMMT, the defects including holes and cracks generated on the surface of the marked one lead to the decreased mechanical property. The desirable combination of high contrast laser marking performance and mechanical properties can be achieved at an OMMT loading content of 2 wt % and a laser current intensity of 9 A. This research work provides a simple, economical, and environmentally friendly method for laser marking of engineering materials such as ABS.

13.
J Clin Anesth ; 61: 109651, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31761416

RESUMO

STUDY OBJECTIVE: Regional anesthesia can improve postoperative analgesia and enhance the quality of recovery (QoR) after surgery. This trial evaluates the effects of ultrasound-guided bilateral superficial cervical plexus block (SCPB) on QoR in patients undergoing thyroid cancer surgery. DESIGN: Prospective, randomized, double-blinded, placebo-controlled trial. SETTING: Operating room. PATIENTS: Seventy-four ASA I-II female patients scheduled for thyroid cancer surgery were included to the study. INTERVENTIONS: Patients were randomly allocated to receive pre-operative ultrasound-guided bilateral SCPB with 10 ml of ropivacaine 0.5% or normal saline on each side. MEASUREMENTS: The primary endpoint was the quality of recovery, which was assessed using the 15-item quality of recovery questionnaire (QoR-15). Secondary endpoints were acute postoperative pain, time to first rescue analgesia, the number of patients requiring rescue analgesia, length of post-anesthesia care unit (PACU) stay, the incidence of postoperative nausea or vomiting (PONV) and dizziness, and patient satisfaction. MAIN RESULTS: The global QoR-15 score at 24 h postoperatively was significantly higher in the SCPB group (Median [IQR], 118 [115-120]) than the control group (110 [106-112]) with a median difference of 8 (95% CI: 6 to 10, P < .001). Compared with the control group, pre-operative ultrasound-guided bilateral SCPB reduced postoperative pain up to 24 h and the incidence of PONV, as well as the length of PACU stay. Additionally, the patient satisfaction scores were improved in the SCPB group (P = .024). CONCLUSION: Pre-operative ultrasound-guided bilateral SCPB with ropivacaine enhances the quality of recovery, postoperative analgesia and patient satisfaction, alleviates the incidence of PONV, and accelerates the PACU discharge following thyroid cancer surgery.


Assuntos
Bloqueio do Plexo Cervical , Bloqueio Nervoso , Neoplasias da Glândula Tireoide , Anestésicos Locais , Bloqueio do Plexo Cervical/efeitos adversos , Método Duplo-Cego , Feminino , Humanos , Bloqueio Nervoso/efeitos adversos , Medição da Dor , Dor Pós-Operatória/epidemiologia , Dor Pós-Operatória/etiologia , Dor Pós-Operatória/prevenção & controle , Estudos Prospectivos , Neoplasias da Glândula Tireoide/cirurgia , Ultrassonografia de Intervenção
14.
Chem Commun (Camb) ; 55(90): 13606-13609, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31657387

RESUMO

Tracking inorganic photochemistry with high resolution poses considerable challenges. Here, sub-picosecond electronic and structural motions and MLCT/d-d intersystem crossing in a cationic iron-porphyrazine are probed using ultrafast transient absorption, stimulated Raman spectroscopy, and quantum calculations. By delineating photoinduced energy relaxation, strategies for extending the lifetime of MLCT state are discussed.

15.
J Am Chem Soc ; 139(43): 15407-15413, 2017 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-28976738

RESUMO

Organic isocyanates are versatile intermediates that provide access to a wide range of functionalities. In this work, we have developed the first synthetic method for preparing aliphatic isocyanates via direct C-H activation. This method proceeds efficiently at room temperature and can be applied to functionalize secondary, tertiary, and benzylic C-H bonds with good yields and functional group compatibility. Moreover, the isocyanate products can be readily converted to substituted ureas without isolation, demonstrating the synthetic potential of the method. To study the reaction mechanism, we have synthesized and characterized a rare MnIV-NCO intermediate and demonstrated its ability to transfer the isocyanate moiety to alkyl radicals. Using EPR spectroscopy, we have directly observed a MnIV intermediate under catalytic conditions. Isocyanation of celestolide with a chiral manganese salen catalyst followed by trapping with aniline afforded the urea product in 51% enantiomeric excess. This represents the only example of an asymmetric synthesis of an organic urea via C-H activation. When combined with our DFT calculations, these results clearly demonstrate that the C-NCO bond was formed through capture of a substrate radical by a MnIV-NCO intermediate.

16.
J Am Chem Soc ; 139(11): 3938-3941, 2017 03 22.
Artigo em Inglês | MEDLINE | ID: mdl-28245648

RESUMO

A reactive hydroxoferric porphyrazine complex, [(PyPz)FeIII(OH) (OH2)]4+ (1, PyPz = tetramethyl-2,3-pyridino porphyrazine), has been prepared via one-electron oxidation of the corresponding ferrous species [(PyPz)FeII(OH2)2]4+ (2). Electrochemical analysis revealed a pH-dependent and remarkably high FeIII-OH/FeII-OH2 reduction potential of 680 mV vs Ag/AgCl at pH 5.2. Nernstian behavior from pH 2 to pH 8 indicates a one-proton, one-electron interconversion throughout that range. The O-H bond dissociation energy of the FeII-OH2 complex was estimated to be 84 kcal mol-1. Accordingly, 1 reacts rapidly with a panel of substrates via C-H hydrogen atom transfer (HAT), reducing 1 to [(PyPz)FeII(OH2)2]4+ (2). The second-order rate constant for the reaction of [(PyPz)FeIII(OH) (OH2)]4+ with xanthene was 2.22 × 103 M-1 s-1, 5-6 orders of magnitude faster than other reported FeIII-OH complexes and faster than many ferryl complexes.


Assuntos
Compostos Ferrosos/química , Hidrogênio/química , Porfirinas/química , Técnicas Eletroquímicas , Entropia , Concentração de Íons de Hidrogênio , Estrutura Molecular
17.
J Org Chem ; 78(10): 5001-6, 2013 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-23611365

RESUMO

Diaryl thioethers and S-cycles were obtained on the basis of the copper-catalyzed reaction of carbon disulfide and aryl iodides in the presence of DBU. This reaction enables the one-pot synthesis of diaryl thioethers by employing cheap, available, and easy-to-handle carbon disulfide with aryl iodides. The reaction was successfully employed in the construction of sulfur-containing cyclic molecules.


Assuntos
Compostos Bicíclicos Heterocíclicos com Pontes/química , Dissulfeto de Carbono/química , Cobre/química , Hidrocarbonetos Iodados/química , Sulfetos/síntese química , Catálise , Estrutura Molecular , Sulfetos/química
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